I think the minimum edge padding(dilation) to use is: log2(max(width,height)) + 1 = nMipmap Levels + 1 for example... for a 2k x 2k texture is (12+1) = 13 in that way it's guaranteed that if two pixels use the maximum and minimum mipmap LOD then a 2x2 box filter result won't present visible seams. The default in xNormal is…
I use 6 on 512x512 (my standard map size, I think I'm a dinosaur) because at one mip down it gives me 3px, at the next down mip down it gives me 1. It's pretty rare for my textures to be mipped more then 3 levels and if it is, and I notice a problem I pad that specific area a little. Going nuts with the padding for those…